Tiny earthquakes may follow groundwater loss

Draining California’s aquifers may stress San Andreas Fault

A GPS station in California’s eastern Sierra Nevada inches up and down slightly as the mountains rise and fall. The mountains’ tiny movements may be influenced by groundwater pumping in the state’s Central Valley. The water loss may also set off little earthquakes along the San Andreas Fault.

As humans drain aquifers in the state’s Central Valley, the land — free of water weight — flexes upward, lifting the surrounding mountain ranges and possibly triggering tiny earthquakes, researchers suggest May 14 in Nature.

It’s the first time scientists have linked the region’s extensive groundwater pumping to mountain uplift and seismic activity, says geophysicist Kristy Tiampo of the University of Western Ontario in London, Canada.

Researchers have known for years that, compared with wet months, dry times see more earthquakes near Parkfield, Calif., a tiny town smack dab in the middle of the state’s biggest seismic hazard, the San Andreas Fault. The fault is the main boundary between two tectonic plates, the rigid sections of Earth’s crust and underlying rocks that can slide past one another.

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